The present invention relates generally to the field of systems and methods for signal detection. More particularly, the present invention relates to a system and method for very low signal to noise ratio signal extraction for spread spectrum signals based on an angle of arrival of the signals.
This application has particular application in SIGINT, COMINT, and ELINT applications where it is desirable to detect a spread spectrum signal and to determine its angle-of-arrival without requiring a priori information concerning the signal.
SIGINT is intelligence-gathering by interception of signals, whether between people (i.e., COMINT or communications intelligence) or between machines (i.e., ELINT or electronic intelligence), or mixtures of the two. Communications intelligence (COMINT) is a sub-category of signals intelligence that engages in dealing with messages or voice information derived from the interception of foreign communications. Electronic signals intelligence (ELINT) is intelligence gathering by use of electronic sensors.
The data that is available from SIGINT may reveal information about an opponent's defense network, especially the electronic parts such as radars, surface-to-air missile systems, aircraft, etc. SIGINT can be used to detect ships and aircraft by their radar and other electromagnetic radiation. SIGINT can be collected from ground stations near the opponent's territory, ships off their coast, aircraft near or in their airspace, or by satellite.
In addition to the content of signals, SIGINT provides information based on both type of electronic transmission and its originating location. Triangulation and more sophisticated radiolocation techniques, such as time of arrival methods, require multiple receiving points at different locations. These receivers send location-relevant information to a central point, or perhaps to a distributed system in which all participate, such that the information can be correlated and a location computed.
Phase interferometry is the technique of using the pattern of interference created by the superposition of two or more waves to diagnose the properties of the aforementioned waves. A phase interferometer may be used to provide precise angle-of-arrival information for radio frequency (RF) signals of interest.
However, spread spectrum signals are often difficult to detect by traditional direction finding techniques since the signal to noise ratio (SNR) at any given time, and at any given frequency, can be very low or even negative. What is needed is a system and method for signal extraction based on their angle of arrival, independent of the signals frequency and modulation phase agility, and at very low signal-to-noise ratios. What is further needed is such a system and method where no apriori information about the signal(s) is required.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.